This invention relates to an improvement in a magnetic disk cartridge.
A magnetic disk cartridge has a diameter substantially equal to that of a floppy disk, but has a larger memory capacity, and can be driven at a higher speed. Moreover, access to its memory surface can be made by the use of a floating type of head. For these reasons, the magnetic disk cartridge has drawn increasing attention as a memory medium for a small computer and which could replace the floppy disk.
A prior-art magnetic disk cartridge has a construction such as shown in FIG. 1. The cartridge includes a magnetic disk 2 which is rotatably accommodated in a plastic cartridge case, and a disk hub 3 functioning also as an armature, and which holds firmly the center of rotation of the magnetic disk 2 and projects from an opening 1a defined in the bottom of the cartridge case. A latching lever 5 has a rear end portion pressed against the inner bottom surface of the case 1 by a leaf spring 4 and a forward end portion pressed into contact with a flange 3a formed around the disk hub 3, in such a manner that it fixes the disk hub 3 to the inner bottom surface of the cartridge case 1.
The disk hub 3 is held firmly in the case 1 together with the magnetic disk 2 by the latching lever 5 when the magnetic disk cartridge is not in use (shown on the left-hand side of FIG. 1).
When the cartridge case 1 is loaded into a magnetic disk driver, a release pin 6 provided in the driver pushes up a holding pin 5a of the latching lever 5, releasing the pressure on the disk hub 3. At the same time, an electromagnetic clutch provided at the end of a spindle motor 7 engages the lower surface of the hub 3, and the spindle motor 7 drives the magnetic disk to rotate at high speed (shown on the right-hand side of FIG. 1).
In a cartridge of this kind, however, there is a large dimensional tolerance between the diameter of the opening 1a and the outer diameter of the disk hub 3, and a wide gap is defined between them. This results in the problem that, even though the magnetic disk 2 and the disk hub 3 are held against the inner bottom of the cartridge case 1 by the spring force of the spring 4, the disk hub 3 can be displaced when handled or shaken roughly, so that the gap at the joint therebetween opens, and contamination due to dust, etc., enters in the cartridge case 1.
Contamination can also occur as a result of wear of the inner bottom portion of the plastic cartridge case 1 against the disk hub 3, which is made of a different material, for example, iron.
In a magnetic disk cartridge of this kind, the occurrence of contamination is a crucial problem. Since the magnetic disk is driven to rotate at high speed, the head is arranged to float by dynamic pressure while keeping at a distance of 0.3 .mu.m from the magnetic disk. If fine dust enters the cartridge case, both the head and the recording surface could be damaged, so that data written on the disk will be destroyed, and head crashes as well as access errors will, occur.